Hi,
Thanks for the explaination.
I still don’t quite get this:
“So in short slowing down the motion by increasing tEnd removes the
dynamic effects of this problem and the rigth muscles will be
activated first as expected for a slow motion.”
–when the segment swing to the right, shouldn’t this motion is cause
by the contraction of the right muscle (no matter how fast it move)?
why when it is moving fast, the right muscle is not being activate
first (in this case, what causes the movement?)?
Another question regarding this:
" The normal muscles in AnyBody can not produce any negative force
(push), so there is no negative force appearing in the muscle
calcualtion at any time, there is no output which are set to zero. If
the muscle can not reduce the overall activity level of the model it
will not be activated, so it is either positive or zero."
–How about the passive force? will the built-up passive force in the
right muscle during its swinging motion to the right helps to ‘push’
the segment to the left when the motion is going to the left (like
the compressed spring does when it was release)?
My assumption is this:
During the ‘swinging right motion’, the contractile muscle in the
right mucle contracts, producing a force to move the segment–this
force also need to overcome the built-up passive force in the right
mucle(due to contraction), and also the built-up passive force in the
left muscle (due to the elongation of the left muscle). When the
segment reach the right most position and starts to swing to the left
, the left muscle contract–but it doesn’t need that much of force
because the gravity, the passive force in the right and left muscles
all contribute to this left swinging motion at that instant. The left
muscle will need more force when the segment pass throught the bottom
position: since now the passive force in both muscle and the gravity
force act in the opposite direction of the left muscle contraction
force.
–Am I right about this? Please let me know if my understanding is
wrong–that muscle doesn’t act in the manner I explain. Or if AnyBody
didn’t take into account of it?
Thank you very much in your time!
Thanks,
Leng-Feng
— AnyBody Support <support@anybodytech.com> wrote:
> Hi Leng-Feng
>
> I think i messed up right and left in that comment it should have
> been left instead of right there. I also wrote
>
> “If gradually increase the tEnd time of the analysis (this is a
> value you can set in your study) you will see that about tEnd=2.5
> sec the right muscles starts to be activated first”
>
> It is correct that by increasing tEnd the motion cn be slowed down.
>
> So in short slowing down the motion by increasing tEnd removes the
> dynamic effects of this problem and the rigth muscles will be
> activated first as expected for a slow motion.
>
> The normal muscles in AnyBody can not produce any negative force
> (push), so there is no negative force appearing in the muscle
> calcualtion at any time, there is no output which are set to zero.
> If the muscle can not reduce the overall activity level of the
> model
> it will not be activated, so it is either positive or zero.
>
> It is another story about the AnyGeneralMuscles these can be
> configured to be able to push.
>
> When the muscle is calibrated the tendon length is adjusted so that
>
> it will have its maximum strength at that particular postion. This
> is done by looking at the overall length of the muscle and
> subtracting the contractile element length to obtain the tendon
> length. So even when the muscle is elongated at zero activity it
> will build up a force in the tendon and passive element. When the
> muscle is shorter than the calibrated length, it will not build up
> any pushing force at zero activity, it will just be relaxed.
>
>
> Best regards
> AnyBody Support
>
> — In anyscript@yahoogroups.com, Leng-Feng Lee <lengfenglee@…>
> wrote:
> >
> > Hi,
> >
> > You said:
> > “So when the motion is too fast the rigth muscle will be actiated
> > first because it has to brake the motion and change the direction
>
> of
> > it.”
> >
> > when you do this:
> > Freq = 2/Main.OneLegStudy.tEnd ;
> >
> > and increase tEnd to 2.5sec or 10 sec, this is actually ‘slowing
> > down’ the motion, right? if tEnd is 1 sec, the motion has to
> complete
> > two cycles in one minutes, so it has to move faster. Instead, if
> the
> > tEnd is 10 sec, it took 10 sec to complete two cycles–this
> motion
> > will be slower. I am confused…
> >
> > also, my previous question:
> > And, am I right that the “negative valued” force in the muscle
> will
> > shown as ‘zero’ in the plotted force profile? If so, does the
> anybody
> > computation machines take the ‘negative valued’ force into
> account
> > when it does the subsequence computation or it will take ‘zero’
> as a
> > value?
> >
> > Another question:
> > When we calibrate the muscle, is it true that we when we do this,
>
> the
> > spring elements in the muscle is at its rest length? such that
> when
> > the muscle is elongated, it create a ‘pulling/contraction’ force
> > opposing the direction of pull; if the muscle is shorten, it
> create a
> > ‘repulsive/pushing’ force that oppose the direction of
> shortening?
> >
> > Thanks for the time in answering so many questions.
> >
> > Thanks,
> > Leng-Feng
> >
> >
> > — AnyBody Support <support@…> wrote:
> >
> > > Hi Leng-Feng
> > >
> > > Nice little model i have taken a look at it.
> > >
> > > There is nothing worng with the muscle parameters, it is the
> > > dynamics effects of teh kinematics that makes the trick here.
> > >
> > > If you change the driver sligthly to be dependent on the tEnd
> value
> > >
> > > of the analysis like this
> > >
> > > AnyKinEqFourierDriver Driver = {
> > > Type = Sin;
> > > Freq = 2/Main.OneLegStudy.tEnd ; //# of cycles
> complete
> > > in 1 sec
> > > A = {{0,1/2}}; //Control the amplitude of swing
> > > B = {{0,0}};
> > > AnyRevoluteJoint &Joint = Main.OneLegModel.Jnts.LegJoint;
> > > Reaction.Type = {Off};
> > > };
> > >
> > > If gradually increase the tEnd time of the analysis (this is a
> > > value
> > > you can set in your study) you will see that about tEnd=2.5 sec
>
> the
> > >
> > > right muscles statrts to be activated first.When you increase
> tEnd
> > > to 10 sec you have the bell shapes you are looking for i
> belive.
> > >
> > > So when the motion is too fast the rigth muscle will be
> actiated
> > > first because it has to brake the motion and change the
> direction
> > > of
> > > it.
> > >
> > > Our normal muscles can not have pushing forces this not
> possible
> in
> > >
> > > any way, but the AnyGeneralMuscles can be set to act like a
> pushing
> > >
> > > element, this is done be setting their ForceDirection paramter
> to
> > > 1.
> > >
> > > Best regards
> > > AnyBody Support
> > >
> > > — In anyscript@yahoogroups.com, Leng-Feng Lee <lengfenglee@>
> > > wrote:
> > > >
> > > > Hi,
> > > >
> > > > Thanks for the quick reply and the demo.
> > > >
> > > > To better understand my problem at hand, I have uploaded a
> model
> > > call
> > > > “OneSegModel.any”, which uses two muscles to move a pivoted
> > > segment
> > > > swinging back and forth.
> > > >
> > > > The muscles are calibrated at its initial position, then run
> the
> > > > simulation. After the simulation, the muscle forces Ft/Fm
> both
> > > have
> > > > the similar profile, as the Passive force Fp.
> > > >
> > > > It is strange that when the segment swing to the right, this
> > > movement
> > > > should be cause by the contraction of the right muscle, but
> > > instead
> > > > the muscle force profile of the right muscle is zero at this
> > > > interval–but when look at muscle force profile of the left
> > > muscle,
> > > > it has a bell curve. I wonder why this is so? It act as if
> > > the ‘swing
> > > > to the right’ motion is cause (push) by the passive force in
> the
> > > Left
> > > > muscle (?).
> > > >
> > > > I guess (?) my muscle model parameters didn’t set up
> correctly
> > > such
> > > > that after the calibration, there are still a lot of passive
> > > force
> > > in
> > > > the muscle? Or what could be the problem?
> > > >
> > > > And, am I right that the “negative valued” force in the
> muscle
> > > will
> > > > shown as ‘zero’ in the plotted force profile? If so, does the
>
> > > anybody
> > > > computation machines take the ‘negative valued’ force into
> > > account
> > > > when it does the subsequence computation or it will take
> ‘zero’
> > > as
> > > a
> > > > value?
> > > >
> > > > Many thanks,
> > > > Leng-Feng
> > > >
> > > > — AnyBody Support <support@> wrote:
> > > >
> > > > > Hi Leng-Feng
> > > > >
> > > > > I have uploaded a small example named
> > > “MuscleModel3eLengFeng.any”
> > > > > to
> > > > > the file section of the group.
> > > > >
> > > > > It is a small model to demonstrate the 3 element hill
> muscle
> > > model.
> > > > > The model consist of one mass which is attached to the
> global
> > > ref
> > > > > using a prismatic joint the mass is hanging in a muscle
> which
> > > will
> > > > > lift the mass upward when running the anlysis.
> > > > >
> > > > > To run the model please calibrate first then run the
> inverse
> > > anal.
> > > > >
> > > > > In the current state of the model the mass of the segment
> is
> 6
> > > kg
> > > > > This will give activity slightly above one
> > > > > The passive force will have a value in the two first steps
> but
> > > it
> > > > > is
> > > > > very small
> > > > > time step1 Fp=0.0155 N
> > > > > time step2 Fp=0.0036 N
> > > > > time step3 Fp=0
> > > > >
> > > > > If you now try to change the mass of the segment to almost
> zero
> > >
> > > > > Mass=0.05 kg
> > > > > Then rerun the analysis you will get these results for the
> > > first
> > > > > steps
> > > > > Activity = 0.053
> > > > > Passive Force Fp=0.131
> > > > > The passive force will continue to have values until
> timestep
> > > 11
> > > > >
> > > > > It may seem strange that the passive force is biggest in
> the
> > > case
> > > > > with the small mass, here is the explanation:
> > > > >
> > > > > When the calibration is preformed we optimize the muscle to
> > > have
> > > > > its
> > > > > optimal strength at the length in which it is calibrated.
> We
> > > simply
> > > > >
> > > > > take the overall length from origin to insertation and
> subtract
> > >
> > > the
> > > > >
> > > > > lenght of the contractile element to obtain the tendon
> length.
> > > > > However we also take into account the strain of the muscle
> when
> > >
> > > it
> > > > > is maximally loaded, when we do the calibration.
> > > > > This means that teoretically the passive force should be
> zero
> > > when
> > > > > the activity is one, this is also what the results of the
> > > analysis
> > > > > shows. The explanation of why it do not give exactly zero
> is
> > > the
> > > > > non linearities in the muscle model.
> > > > >
> > > > > Then the question why do the model with the small mass give
> a
> > > > > larger
> > > > > passive force?
> > > > > When the muscle is loaded with the weight of a small mass,
> the
> > > > > tendon will be shorter than the calibrated length because
> in
> > > the
> > > > > calibrated length the strain of the tendon for activity one
> > > > > is taken into account. In other words: the muscle is
> calibrated
> > >
> > > for
> > > > >
> > > > > activity one. Since we in both cases drive the overall
> lengh
> of
> > >
> > > the
> > > > >
> > > > > muscle to the same length the passive element will be more
> > > > > strecthed
> > > > > in the case where we have the small mass, because the
> tendon
> is
> > >
> > > not
> > > > >
> > > > > loaded so much.
> > > > >
> > > > > So you may ask why did we choose to take into account the
> > > tendon
> > > > > strain when we calibrate the muscle?
> > > > > This we did because we wanted to have the optimum strength
> > > exactly
> > > > > at the calibrated length this would not have been the
> result
> > > > > otherwise.
> > > > >
> > > > > The passive element should work exactly as you describe in
> the
> > > end
> > > > > of your email, but when the muscle is not loaded very much
> the
> > > > > passive force will not be zero at the calibrated length.
> > > > > Furthermore
> > > > > the parameters of your model enhance this phenomean because
> > > your
> > > > > tendon length is extremely long.
> > > > >
> > > > >
> > > > > I hope this answers your question otherwise please do not
> > > hesitate
> > > > > to write again.
> > > > >
> > > > > Best regards
> > > > > AnyBody Support
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > — In anyscript@yahoogroups.com, “Leng-Feng Lee”
> > > <lengfenglee@>
> > > > >
> > > > > wrote:
> > > > > >
> > > > > > Hello,
> > > > > >
> > > > > > I have a muscle modeled using AnyMuscleModel3E, it is
> connect
> > >
> > > > > through
> > > > > > viapointmuscle and the distance between the two points it
> > > > > connects
> > > > > is
> > > > > > 0.5m. I gave the following properties for it:
> > > > > >
> > > > > > AnyMuscleModel3E MuscleModelC = {
> > > > > > F0 = 100;
> > > > > > Lfbar = 0.5;
> > > > > > Lt0 = 0.5;
> > > > > > Epsilonbar = 0.05;
> > > > > > Gammabar = 30*pi/180; //Pennation Angle
> > > > > > Fcfast = 0.4; //Fraction of fast twitch
> > > fibers
> > > > > > Jt = 3.0; //Elasiticity of tendon
> > > (serial)
> > > > > > Jpe = 3.0; //Elasiticity of tendon
> > > (Parallel)
> > > > > > K1 = 2;
> > > > > > K2 = 8;
> > > > > > PEFactor = 5;
> > > > > > };
> > > > > >
> > > > > > It contract to lift up a segment connected to a joint-no
> > > external
> > > > >
> > > > > load.
> > > > > >
> > > > > > My problem is that the passive force appear throughout
> the
> > > > > > simulation—something not desired.
> > > > > >
> > > > > > I calibrated the muscle at the initial position, and try
> to
> > > > > change
> > > > > the
> > > > > > Lfbar and Lt0 value, but the passive force still exist
> > > throughout
> > > > >
> > > > > the
> > > > > > simulation.
> > > > > >
> > > > > > I would like to have a passive force to act in the
> following
> > > way:
> > > > >
> > > > > at
> > > > > > the initial stage, there is no passive force, as the
> muscle
> > > > > contract,
> > > > > > the passive force store up(like compressing a spring) and
>
> act
> > >
> > > in
> > > > > a
> > > > > > direction opposing the contracting force(?), and as the
> > > motion
> > > > > change
> > > > > > direction, the passive force release(like let go a
> compressed
> > >
> > > > > spring).
> > > > > >
> > > > > > Could this be done? What parameter(s) should I
> change/adjust?
> > >
> > > Or
> > > > > my
> > > > > > concept about the muscle modeling is wrong? Detail
> > > explaination
> > > > > > greately appreciated.
> > > > > >
> > > > > > Thanks,
> > > > > > Leng-Feng
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > > >
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